The invention relates to a homogenization and heating container for a liquid working fluid, in particular a liquid component mixed with additives of a plastics injection molding apparatus.
Known containers of this type, as used in conjunction with polyurethane injection molding plants for heating and homogenizing the polyol component, typically mixed with additives such as activators, stabilizers and blowing agents or also milled fibers or powdered minerals, include an outer container casing, which is normally supplied with water as heat carrier, for temperature control, and a compressed gas cushion, provided above the liquid level in the container, for maintaining a defined container pressure and for compensating fluctuations in the filling amount. A high product quality requires an extremely even and exact heating and homogenization of the polyol component, even though the throughput of polyol, in relation to the load capacity of the container, is, in general, very low. Thus, the provision of an agitator is necessary to conduct the polyol fill at high circulating speed along the container casing, which is heated and cooled by the heat carrier, and to implement a thorough mixing. Such an agitator represents, however, a disturbing heat source, has a complicated structure, and increases the energy need, and furthermore risks forced inclusion of gas particles from the gas cushion into the polyol component with resultant foaming thereof.
It is an object of the invention to provide a homogenization and heating container of the above-stated type, which is simpler in construction and more energy-efficient while yet maintaining a high product quality.
This object is attained in accordance with the invention by the homogenization and heating container which includes a heat exchanger for heating the working medium and a recirculation pump for returning the working medium from the container outlet to the container inlet, wherein the heat exchanger, which is dipped in the working medium inside the container, is arranged at a distance to the container wall and enclosed by at least one partition wall which so subdivides the container in concentric annular spaces that the flow path of the recirculated working medium runs in counterflow direction through the heat exchanger and the annular spaces.
In accordance with the invention, the subdivision of the container volume into several annular spaces, through which recirculated working medium flows sequentially in counterflow direction, in conjunction with the forced inclusion of the inner surfaces as well as the outer surfaces of the heat exchanger into the counterflow path, results not only in a reduction of heat losses of the heat exchanger and effective increase of the heat exchange surfaces, but realizes also high flow velocities inside the container, even at slight container throughputs, and an intimate contact and a thorough mixing of the recirculated working medium with the container content, without requiring a complex and energy-intensive agitator. Thus, the container according to the invention is significantly simplified in construction, exhibits reduced energy consumption and, at the same time, effectively counteracts the risk of foaming of the liquid component in the container.
In the event, a gas or air cushion is generated in the homogenization and heating container above the liquid level, as is typically the case in a polyurethane injection molding apparatus, the partition wall suitably extends with its upper rim beyond the liquid level in the container so that the liquid flow runs in the area of the upper rim of the partition wall along this upper rim to thereby even out the flow distribution during transfer between neighboring annular spaces and to further enhance the degree of mixing.
According to a further, particularly preferred configuration of the invention, the heat exchanger is arranged upstream of the annular spaces in the inlet zone of the container, i.e. at a location where a temperature equalization has not yet occurred between the recirculated working medium and the container content so that the difference of the temperature of the working medium and the desired temperature is the greatest, thereby realizing a high temperature gradient at the heat exchanger and thus an even more efficient use of the heat exchange surfaces.
Preferably, a plate heat exchanger, or a tubular heat exchanger is used as heat exchanger.
Particularly suitable, is the disposition of a plate, at least in the inlet region of one of the annular spaces, for creating a cross sectional constriction, thereby realizing a local acceleration of the flow and deflection of the flow to the center of the annular space. This further significantly enhances the homogenization and heating effect of the container. In particular advantageous is the split of the flow into a plurality of single streams. This can be implemented in a structurally simple manner by configuring the plate as an annular collar which extends transversely to the partition wall and has a plurality of holes, or is provided with a serrated or corrugated flow-by edge.